Due to changes in Dropbox's service offerings, a quota of 200GB is being instituted as of October 1, 2018. Notifications have been turned on now to give you a chance to get under quota by then. They look something like this:
Your MIT account is full
Your dropbox account space is full
This warning does not limit your ability to use Dropbox in any way, even if you are near or over the quota. You are still able to access all of your files, upload new files, sync files, and otherwise use Dropbox as you did before. The informational quota allows you to check your current usage within the limit that will be imposed in October.
Once the quota is enforced in October, you will be unable to upload additional files while over quota. Existing files will not be removed and will continue to be accessible (although may not be updated or changed until the account is below quota). The error seen when trying to upload additional files or update existing files when over quota looks something like these:
In order to upload or update any of your files in Dropbox, you must first get below quota.